The present invention relates to novel polymeric actuators and a process for producing the same. More particularly, the invention relates to polymeric actuators functioning as actuators by bending or deforming ion-exchange resin products and to a process for producing the polymeric actuators.
Recently, there is an enhanced demand for a miniaturized, lightweight and highly flexible actuator in the fields of medical equipment, industrial robots, micromachines and the like.
When the actuator is thus miniaturized, the friction and viscous force are dominant over the inertial force. Therefore, it has been difficult to employ the means for converting energy to motion with the use of inertial force, such as a motor or an engine, as the power source of a microactuator. Accordingly, the operating principles based on electrostatic attraction, piezoelectricity, ultrasonic wave, shape memory alloy and polymer expansion/contraction have been proposed for the microactuator.
The actuator of the electrostatic attraction type operates by attracting, for example, a plate or rod becoming an electrode toward a counter electrode, and, for example, one which bends an electrode by applying a voltage of about 100 V between the electrode and the counter electrode disposed with a spacing of about tens of microns is known. The piezoelectric actuator operates by applying a voltage of some volts to a piezoelectric element of a ceramic such as barium titanate so that the element is expanded and contracted, and one capable of controlling a nm-unit displacement is known. The ultrasonic actuator operates by combining frictional force with the ultrasonic vibration generated by the piezoelectric element or the like, or by effecting a runoff. The actuator of the shape memory alloy type operates by temperature change with the use of the marked change of the configuration of the shape memory alloy depending on temperature. The actuator of the polymer expansion/contraction type operates with the use of the expansion/contraction of the polymer depending on the temperature or change of pH and change of the concentration of environmental chemical substance.
However, these microactuators have drawbacks in that there is restriction in their respective operation environments, the response is unsatisfactory, the structure is complicated and the flexibility is poor. For example, for the operation of the actuator of the polymer expansion/contraction type, the solution in contact with the polymer must be replaced by the solution containing other salt. Therefore, it has been difficult to employ this actuator in the use requiring a small size and a rapid response.
In contrast, an actuator element comprising an ion-exchange membrane and electrodes coupled to surfaces of the ion-exchange membrane and adapted to apply a potential difference to the ion-exchange membrane in the hydrous state so that the ion-exchange membrane is curved or deformed has been proposed as one which can be easily miniaturized, realizes rapid response and operates with small electric power (see Japanese Patent Laid-open Publication No. 4(1992)-275078).
This actuator element is characterized by comprising an ion-exchange resin membrane (ion-exchange resin molding) and metal electrodes coupled to surfaces thereof in mutually insulating relationship and by being adapted to apply a potential difference between the metal electrodes while the ion-exchange resin membrane is in the hydrous state so that the ion-exchange resin membrane is curved or deformed.
In this actuator element, the electrodes are formed on the surfaces of the ion-exchange resin molding by chemical plating, electroplating, vacuum deposition, sputtering, coating, press bonding, fusion bonding or other methods. For example, the conventional process for forming the electrodes by the chemical plating includes a process comprising subjecting the ion-exchange membrane to etching of the surfaces thereof, bearing of a plating catalyst and immersion in a plating bath, thereby to form electrodes on the surfaces of the ion-exchange membrane and a process comprising the steps of making the surfaces of the ion-exchange resin membrane to adsorb a metal complex, followed by reducing the adsorbed complex, and then immersing the ion-exchange resin membrane in a plating bath to form the electrodes on the surfaces of the ion-exchange membrane.
However, the actuator element having the electrodes formed by the above methods has a drawback in that the displacement level is not satisfactory. In the conventional polymeric actuator, further, when the voltage applied between the electrodes is increased to obtain larger displacement and better response, water in the ion-exchange resin membrane is easily electrolyzed, and therefore bubbles are easily produced.
The present invention is intended to solve such problems associated with the prior art as mentioned above, and it is an object of the invention to provide an actuator element capable of generating large displacement, having rapid response and high flexibility, having simple structure and capable of being easily miniaturized, and a process for producing the same. It is another object of the present invention to provide a polymeric actuator free from occurrence of bubbles due to electrolysis of water when a potential difference is applied.
The process for producing a polymeric actuator according to the present invention is a process for producing a polymeric actuator comprising an ion-exchange resin product and metal electrodes which are formed on the surface of the ion-exchange resin product and are insulated from each other, said polymeric actuator operating as an actuator by applying a potential difference between the metal electrodes when the ion-exchange resin product is in the water-containing state to allow the ion-exchange resin product to undergo bending or deformation,
wherein the following steps (i) to (iii) are repeatedly conducted to form the metal electrodes ranging from the surface of the ion-exchange resin product to the inside thereof;
(i) a step of allowing the ion-exchange resin product to adsorb a metal complex in an aqueous solution (adsorption step),
(ii) a step of reducing the metal complex adsorbed on the ion-exchange resin product by a reducing agent to deposit a metal on the surface of the ion-exchange resin product (deposition step), and
(iii) a step of washing the ion-exchange resin product having the deposited metal (washing step).
By virtue of the method to form metal electrodes through the above steps, metal deposition further proceeds to the interior of the ion-exchange resin product to increase the contact area between the ion-exchange resin product and the metal electrodes, whereby the number of electrode active spots is increased to thereby increase the quantity of ions which migrate to a negative electrode. In the polymeric actuator, water molecules accompanying the ions migrate to a negative electrode so that the water content in the vicinity of said electrode is decreased to thereby expand the negative electrode side of the resin product, while the water content in the vicinity of the positive electrode is decreased to thereby contract the positive electrode side of the resin product. Accordingly, when the quantity of ions which migrate to an electrode is increased, the quantity of water molecules which migrate to the electrode together with the ions is also increased. As a result, the difference in the water content between the vicinity of the negative electrode and the vicinity of the positive electrode becomes larger, and the degree of bending (deformation), namely, degree of displacement, is increased. Further, since the thickness of the metal electrode is increased, the surface resistance of the electrode is decreased to raise conductivity of the electrode.
According to the process of the invention, therefore, a polymeric actuator having simple structure, capable of being easily miniaturized, showing quick response and capable of generating large displacement can be obtained.
The polymeric actuator according to the present invention comprises an ion-exchange resin product and metal electrodes which are formed on the surface of the ion-exchange resin product containing an alkylammonium ion as a counter ion and are insulated from each other, said polymeric actuator operating as an actuator by applying a potential difference between the metal electrodes when the ion-exchange resin product is in the water-containing state to allow the ion-exchange resin product to undergo bending or deformation.
In the polymeric actuator of the invention, the counter ions of the ion-exchange resin product are exchanged with specific alkylammonium ions, and thereby bubbles are hardly produced even under application of a high voltage, differently from the conventional ion-exchange resins whose counter ion is Na+ or H+. In the polymeric actuator, further, water molecules accompanying the ions generally migrate to an electrode to increase the water content in the vicinity of said electrode. As a result, this electrode side of the resin product is swollen and expanded, while the water content in the vicinity of the opposite electrode is decreased to thereby contract the opposite electrode side of the resin product. Therefore, if the counter ions are exchanged with the alkylammonium ions, the difference in the water-content between the electrodes becomes larger, and the degree of bending (deformation), namely, degree of displacement, can be increased.
It is preferable that, as the alkylammonium ion, an alkylaluminum ion represented by the following formula (1) is contained. When such ions are contained, the difference in the water content between the electrodes becomes much larger, and the degree of bending (deformation), namely, degree of displacement, can be increased. 
In the above formula, R1 to R4 may be the same or different and are each a hydrogen atom, a hydrocarbon group, an oxygen-containing hydrocarbon group or a nitrogen-containing hydrocarbon group, at least one of R1 to R4 is a group other than a hydrogen atom, and two or more of R1 to R4 may be bonded to form a ring.
In the polymeric actuator of the invention, it is more preferable that the alkylammonium ion is represented by the above formula (1), and it is particularly preferable that the alkylammonium ion is CH3N+H3, C2H5N+H3, (CH3)2N+H2, (C2H5)2N+H2, (C4H9)2N+H2, (C5H11)2N+H2, (CH3)3N+H, (C2H5)3N+H, (C4H9)3N+H, (C5H11)3N+H, (CH3)4N+, (C2H5)4N+, (C3H7)4N+, (C4H9)4N+, H3N+(CH2)4N+H3, H2Cxe2x95x90CHCH2N+HCH3, H3N+(CH2)4N+H2(CH2)4N+H3, HCxe2x89xa1CCH2N+H2, CH3CH(OH)CH2N+H3, H3N+(CH2)5OH, H3N+CH(CH2OH)2, (HOCH2)2C(CH2N+H3)2, C2H5OCH2CH2N+H3, 
It is most preferable that the alkylammonium ion is (C4H9)3N+H, (C5H11)3N+H, (C3H7)4N+ or (C4H9)4N+.
The polymeric actuator of the invention has a simple structure and can be easily miniaturized. Further, even if voltage is increased, production of bubbles caused by electrolysis of water present in the resin product can be inhibited. Furthermore, the polymeric actuator shows quick response and can generate large displacement.